The present invention relates to a non-contact movement quantity measurement method and an apparatus therefor, which can be used as a method and an apparatus for measuring fine and impulsive movement, for example, for measuring the quantity of injection of a car diesel injection pump.
Heretofore, the non-contact movement quantity measurement method is classified mainly into an increment type and an absolute type. A moved distance measurement apparatus of the increment type is disclosed in Japanese Patent Post examination publication No. Hei-1-23048. In the measurement apparatus, a slit plate is provided so as to be movable together with a subject to be measured. Light is radiated to the slit plate. The rays of light passed through slits of the slit plate is measured by a light detector so that the number of the passed rays of light is counted to thereby measure the quantity of movement of the slit plate, that is, the quantity of movement of the subject.
On the other hand, a moved distance measurement apparatus of the absolute type is disclosed in Japanese Patent Postexamination publication No. Hei-1-22884. In the measurement apparatus, coded slits are formed in a slit plate which moves together with a subject to be measured. Light is radiated to the slit plate. The rays of light passed through slits in the slit plate is detected by a light detector to thereby detect the position of a slit before the movement of the subject and the position of the slit after the movement of the subject. Distances from a reference position to the respective slits are measured and stored in advance. Accordingly, the quantity of movement of the slit plate can be detected by measuring the positions of the slits through which rays of light pass, after the movement of the slit plate.
The following problems arise in the aforementioned conventional moved distance measurement method and apparatus.
In the increment type, the number of slits passing through the light detector is measured by a counter. Accordingly in the case where the subject moves at a very high speed, the counter cannot follow the high-speed movement of the slits. There arises a problem that the quantity of movement cannot be measured accurately.
On the other hand, in the absolute type, there is no problem in the follow operation. However, not only a moving subject cannot be measured but the minimum measurable quantity of moved distance depends on the slit interval between respective slits formed in the slit plate. Accordingly, as the distance to be measured becomes smaller, it is necessary to make the slit interval narrower physically. There arises a problem that the measurement cannot be applied to the extent of a fine range.